1. Field of the Invention
This invention relates to a silicone crumb which is useful as a hydraulic material.
2. Background Information
Materials used in hydraulic systems were mainly fluid, i.e. gases or liquids. Such systems are used in machines to move parts of the equipment, for example in a hoist to lift automobiles. Other systems using hydraulics are the brakes on vehicles. The use of solid materials for hydraulic purposes is much more limited because most solids do not readily move and transfer pressure as conveniently as gases and liquids. Silicone fluids are used in hydraulic systems but these systems must be closed systems in the same manner as other hydraulic systems using gases or liquids. If the systems using gases or liquids are not closed, loss of material will occur and the effectiveness of the hydraulics is lost.
Other disadvantages of liquids is that if a leak should occur, it may cause undesirable environmental conditions and the cleanup may be difficult. Some liquids may be unstable under high temperature conditions and solidify or deteriorate such that the hydraulic system is ineffective for its purpose.
Solid materials which can be deformed might be suggested as useful material for hydraulic purposes and for use in methods for thermal expansion molding for composites. These thermal expansion molding methods use solid elastomeric materials in molds to cause pressure against a composite during the molding process. Such thermal expansion molding methods have the disadvantage that the determination of the pressure against the composite is difficult and requires very careful filling of the elastomeric mold portion because either under or over filling can cause unwanted pressures which result in bad composites. Because of the difficulty of using solid elastomeric materials in the thermal expansion molding methods, the expense is high enough to cause these methods to be used only in very special applications in which the expense would be acceptable. However, not much is reported for use of solid materials for hydraulic purposes because the solid materials do not flow.
Bruner in U.S. Pat. No. 3,843,601, issued Oct. 22, 1974, describes a hydraulic elastomer which is reported to have a high cross-link density and a high proportion of free chain ends. Bruner crumbles his elastomer under high shear stress to a powder which flows like a viscous fluid through a narrow orifice. Bruner reports that silicone elastomers are desirable materials for their high thermal stability, have high compressibility, and can be forced through an orifice. However, the silicone elastomers do not easily flow back into their original position because they are relatively hard. Oil has been used to plasticize the elastomer but this results in oil bleed which leaks out of the system. Bruner teaches that an improved hydraulic elastomer can be obtained by curing a linear vinyl containing siloxane copolymer which is made up of dimethylsiloxane units and methylvinylsiloxane units and which has a molecular weight between 20,000 and 200,000 corresponding to viscosities between 1000 and 1,000,000 centipoise at 25.degree. C. The vinyl is present in Bruner's copolymer in an amount of from 0.1 to 0.9 mole percent. Bruner teaches that even with the optimum vinyl content it is found that the ultimate properties of the cured elastomers are not as good as when the viscosity of the fluid is at least 5000 cp and that good physical properties are obtained when the viscosity of the fluid reaches 1,000,000 cp. Bruner cures his vinyl containing copolymer with peroxide. Bruner teaches that those cured elastomers of his which have durometers on the Shore A scale of 8, 10, 19, 22, and 26 are outside the acceptable range of hardness which means that the acceptable hardness are those which have durometers on the Shore A scale between 11 and 18.